5,283 research outputs found
Understanding the spin-down rate changes of PSR B0919+06
We study the spin-down properties of PSR B0919+06 based on almost 30 years of
radio observations. We confirm that the time derivative of the rotational
frequency is modulated quasi-periodically and show that it exhibits
a repeating double-peaked structure throughout the entire observation span. We
model the variation of the pulsar assuming two spin-down rates with
sudden switches between them in time. Our results show that the double-peak
structure in has a repetition time of about 630 days until MJD 52000
(April 2001) and 550 days since then. During this cycle, the pulsar spin varies
from the lower spin-down rate to the upper spin-down rate twice with different
amounts of time spent in each state, resulting in a further quasi-stable
secondary modulation of the two-state switching. This particular spin-down
state switching is broadly consistent with free precession of the pulsar,
however, a strong evidence linked with this mechanism is not clearly
established. We also confirm that the pulsar occasionally emits groups of
pulses which appear early in pulse phase, so-called "flares", and these events
significantly contribute to the pulse profile shape. We find the
modulation and the pulse shape variations are correlated throughout the
observations. However, the flare-state is not entirely responsible for this
correlation. In addition to the flare-state, we detect flare-like events from
the pulsar in single pulse observations. During these events, the shift in
pulse phase is small compared to that of the main flare-state and clearly
visible only in single pulse observations.Comment: 10 pages, 12 Figures, Accepted by MNRAS on 10 October 201
Dynamic criticality in glass-forming liquids
We propose that the dynamics of supercooled liquids and the formation of
glasses can be understood from the existence of a zero temperature dynamical
critical point. To support our proposal, we derive from simple physical
assumptions a dynamic field theory for supercooled liquids, which we study
using the renormalization group (RG). Its long time behaviour is dominated by a
zero temperature critical point, which for dimensions d > 2 belongs to the
directed percolation universality class. Molecular dynamics simulations confirm
the existence of dynamic scaling behaviour consistent with the RG predictions.Comment: 4 pages, 2 figure
Сравнение расхода топлива и уровня выбросов при обычной и гибридных конфигурациях трансмиссий c учетом циклов движения и степени гибридизации
Hybrid electric powertrains in automotive applications aim to improve emissions and fuel economy with respect to conventional internal combustion engine vehicles. Variety of design scenarios need to be addressed in designing a hybrid electric vehicle to achieve desired design objectives such as fuel consumption and exhaust gas emissions. The work in this paper presents an analysis of the design objectives for an automobile powertrain with respect to different design scenarios, i. e. target drive cycle and degree of hybridization. Toward these ends, four powertrain configuration models (i. e. internal combustion engine, series, parallel and complex hybrid powertrain configurations) of a small vehicle (motorized three-wheeler) are developed using Model Advisor software and simulated with varied drive cycles and degrees of hybridization. Firstly, the impact of vehicle power control strategy and operational characteristics of the different powertrain configurations are investigated with respect to exhaust gas emissions and fuel consumption. Secondly, the drive cycles are scaled according to kinetic intensity and the relationship between fuel consumption and drive cycles is assessed. Thirdly, three fuel consumption models are developed so that fuel consumption values for a real-world drive cycle may be predicted in regard to each powertrain configuration. The results show that when compared with a conventional powertrain fuel consumption is lower in hybrid vehicles. This work led to the surprisingly result showing higher CO emission levels with hybrid vehicles. Furthermore, fuel consumption of all four powertrains showed a strong correlation with kinetic intensity values of selected drive cycles. It was found that with varied drive cycles the average fuel advantage for each was: series 23 %, parallel 21 %, and complex hybrids 33 %, compared to an IC engine powertrain. The study reveals that performance of hybrid configurations vary significantly with drive cycle and degree of hybridization. The paper also suggests future areas of study
Growing spatial correlations of particle displacements in a simulated liquid on cooling toward the glass transition
We define a correlation function that quantifies the spatial correlation of
single-particle displacements in liquids and amorphous materials. We show for
an equilibrium liquid that this function is related to fluctuations in a bulk
dynamical variable. We evaluate this function using computer simulations of an
equilibrium glass-forming liquid, and show that long range spatial correlations
of displacements emerge and grow on cooling toward the mode coupling critical
temperature
Normalization factors for magnetic relaxation of small particle systems in non-zero magnetic field
We critically discuss relaxation experiments in magnetic systems that can be
characterized in terms of an energy barrier distribution, showing that proper
normalization of the relaxation data is needed whenever curves corresponding to
different temperatures are to be compared. We show how these normalization
factors can be obtained from experimental data by using the
scaling method without making any assumptions about the nature of the energy
barrier distribution. The validity of the procedure is tested using a
ferrofluid of Fe_3O_4 particles.Comment: 5 pages, 6 eps figures added in April 22, to be published in Phys.
Rev. B 55 (1 April 1997
Multi-frequency study of the peculiar pulsars PSR B0919+06 and PSR B1859+07
Since their discovery more than 50 years ago, broadband radio studies of
pulsars have generated a wealth of information about the underlying physics of
radio emission. In order to gain some further insights into this elusive
emission mechanism, we performed a multi-frequency study of two very well-known
pulsars, PSR~B0919+06 and PSR~B1859+07. These pulsars show peculiar radio
emission properties whereby the emission shifts to an earlier rotation phase
before returning to the nominal emission phase in a few tens of pulsar
rotations (also known as `swooshes'). We confirm the previous claim that the
emission during the swoosh is not necessarily absent at low frequencies and the
single pulses during a swoosh show varied behaviour at 220~MHz. We also confirm
that in PSR~B0919+06, the pulses during the swoosh show a chromatic dependence
of the maximum offset from the normal emission phase with the offset following
a consistent relationship with observing frequency. We also observe that the
flux density spectrum of the radio profile during the swoosh is inverted
compared to the normal emission. For PSR~B1859+07, we have discovered a new
mode of emission in the pulsar that is potentially quasi-periodic with a
different periodicity than is seen in its swooshes. We invoke an emission model
previously proposed in the literature and show that this simple model can
explain the macroscopic observed characteristics in both pulsars. We also argue
that pulsars that exhibit similar variability on short timescales may have the
same underlying emission mechanism.Comment: 13 pages, 13 figures, 1 table, accepted for publication in MNRA
Diffusion and viscosity in a supercooled polydisperse system
We have carried out extensive molecular dynamics simulations of a supercooled
polydisperse Lennard-Jones liquid with large variations in temperature at a
fixed pressure. The particles in the system are considered to be polydisperse
both in size and mass. The temperature dependence of the dynamical properties
such as the viscosity () and the self-diffusion coefficients () of
different size particles is studied. Both viscosity and diffusion coefficients
show super-Arrhenius temperature dependence and fit well to the well-known
Vogel-Fulcher-Tammann (VFT) equation. Within the temperature range
investigated, the value of the Angell's fragility parameter (D )
classifies the present system into a strongly fragile liquid. The critical
temperature for diffusion () increases with the size of the
particles. The critical temperature for viscosity () is larger than
that for the diffusion and a sizeable deviations appear for the smaller size
particles implying a decoupling of translational diffusion from viscosity in
deeply supercooled liquid. Indeed, the diffusion shows markedly non-Stokesian
behavior at low temperatures where a highly nonlinear dependence on size is
observed. An inspection of the trajectories of the particles shows that at low
temperatures the motions of both the smallest and largest size particles are
discontinuous (jump-type). However, the crossover from continuous Brownian to
large length hopping motion takes place at shorter time scales for the smaller
size particles.Comment: Revtex4, 7 pages, 8 figure
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