1,442 research outputs found
Impact of turbocharger non-adiabatic operation on engine volumetric efficiency and turbo lag
Turbocharger performance significantly affects the thermodynamic properties of the working fluid at engine boundaries and hence engine performance. Heat transfer takes place under all circumstances during turbocharger operation. This heat transfer affects the power produced by the turbine, the power consumed by the compressor, and the engine volumetric efficiency. Therefore, non-adiabatic turbocharger performance can restrict the engine charging process and hence engine performance. The present research work investigates the effect of turbocharger non-adiabatic performance on the engine charging process and turbo lag. Two passenger car turbochargers are experimentally and theoretically investigated. The effect of turbine casing insulation is also explored. The present investigation shows that thermal energy is transferred to the compressor under all circumstances. At high rotational speeds, thermal energy is first transferred to the compressor and latter from the compressor to the ambient. Therefore, the compressor appears to be "adiabatic" at high rotational speeds despite the complex heat transfer processes inside the compressor. A tangible effect of turbocharger non-adiabatic performance on the charging process is identified at turbocharger part load operation. The turbine power is the most affected operating parameter, followed by the engine volumetric efficiency. Insulating the turbine is recommended for reducing the turbine size and the turbo lag
The Enigma of the Dark Matter
One of the great scientific enigmas still unsolved, the existence of dark
matter, is reviewed. Simple gravitational arguments imply that most of the mass
in the Universe, at least 90%, is some (unknown) non-luminous matter. Some
particle candidates for dark matter are discussed with particular emphasis on
the neutralino, a particle predicted by the supersymmetric extension of the
Standard Model of particle physics. Experiments searching for these relic
particles, carried out by many groups around the world, are also discussed.
These experiments are becoming more sensitive every year and in fact one of the
collaborations claims that the first direct evidence for dark matter has
already been observed.Comment: Invited review article for the journal Contemporary Physics. The
level is suitable for researchers which are non-specialists in the subject,
and also for students. Latex, 20 pages, 5 figure
New shifted hybrid inflation
A new shifted hybrid inflationary scenario is introduced which, in contrast
to the older one, relies only on renormalizable superpotential terms. This
scenario is automatically realized in a concrete extension of the "minimal"
supersymmetric Pati-Salam model which naturally leads to a moderate violation
of Yukawa unification so that, for mu>0, the predicted b-quark mass is
acceptable even with universal boundary conditions. It is shown that this
extended model possesses a classically flat "shifted" trajectory which acquires
a slope via one-loop radiative corrections and can be used as inflationary
path. The constraints from the cosmic background explorer can be met with
natural values of the relevant parameters. Also, there is no disastrous
production of magnetic monopoles after inflation since the Pati-Salam gauge
group is already broken on the "shifted" path. The relevant part of inflation
takes place at values of the inflaton field which are not much smaller than the
"reduced" Planck scale and, thus, supergravity corrections could easily
invalidate inflation. It is, however, shown that inflation can be kept intact
provided that an extra gauge singlet with a superheavy vacuum expectation
value, which originates from D-terms, is introduced and a specific form of the
Kaehler potential is used. Moreover, it is found that, although the
supergravity corrections are sizable, the constraints from the cosmic
background explorer can again be met by readjusting the values of the
parameters which were obtained with global supersymmetry.Comment: 18 pages including 1 figure, uses JHEP3.cls, minor corrections,
version to appear in JHE
Like-sign dimuon charge asymmetry in Randall-Sundurm model
We confirm that in order to account for the recent D\O\ result of large
like-sign dimuon charge asymmetry, a considerable large new physics effect in
is required in addition to a large CP violating phase in mixing. In the Randall-Sundrum model of warped geometry, where the
fermion fields reside in the bulk, new sources of flavor and CP violation are
obtained. We analyze the like-sign dimuon asymmetry in this class of model, as
an example of the desired new physics. We show that the wrong charge asymmetry,
, which is related to the dimuon asymmetry, is significantly altered
compared to the Standard Model value. However, experimental limits from , as well as mixing and electroweak corrections
constrain it to be greater than a away from its experimental average
value. This model cannot fully account for the D\O\ anomaly due to its
inability to generate sufficient new contribution to the width difference
, even though the model can generate large contribution to the
mass difference .Comment: 20 pages, 9 figures, discussions and references added, accepted for
publication in Physical Review
Structural, Morphological and Optical Parameters of Zn(1-x) CuxS Thin Films for Optoelectronic Devices
In the present work, ZnS and Cu incorporated at (2%, 4%,6%, 8%, and 10%) thin films were growth onto hot glass substrates at substrates temperature 270 oC with thickness about 100 nm by chemical spray pyrolysis technique. The solutions of the spray consists of Zn(CH3COO)2.2H2O, SC(NH2)2 and CuCl2.2H2O with molar concentration 0.1M/L. The structure of the film was studied by XRD pattern, the results shows that the films were polycrystalline with cubic phase for pure ZnS and hexagonal phase for Zn1-xCuxS at x=10%. The optical constants, refractive index, n and extinction coefficient, k were determined The optical energy gap of the direct transition is also estimated, pure ZnS is 3.42 eV, and it increases as the Cu concentration increases from 3.49 to 3.67 eV. The room temperature photoluminescence (PL) of copper-doped zinc sulfide (ZnS:Cu) nanoparticles was studied. Through Gaussian fitting, the PL spectrum of undoped ZnS nanoparticles is deconvoluted into two blue luminescence peaks (centered at 411 nm and 455 nm, respectively), both of which can be attributed to the recombination of ZnS defect states. But for doped samples, a third peak at about 500 nm was also identified. Discussed the changes of all optical constants and PL spectra from the changes of optoelectronics microstructure parameter
A Strategy for Emergency Vehicle Preemption and Route Selection
Emergency vehicle preemption (EVP) aims to give right of way to emergency vehicles (EV) heading toward the incident location through a network of signalized intersections by creating a green wave en-route. The design goals of EVP systems are two folds: first, to avoid any hindrance to the passage of EV along the road and at the intersections and second, to reduce the negative impact of preemption on general traffic. The negative impact of EVP on normal traffic can be minimized by selecting appropriate preemption strategy. The EVP schemes proposed earlier aim to minimize the travel time of the EV with no or little consideration to the negative impact of EVP on the normal traffic. In this study, a joint strategy for optimal path selection and EV preemption is developed. The proposed scheme selects the optimal path for the EV before it departs from its origin and then activates the preemption on each intersection en-route at the right time to clear the intersection before the EV reaches. The proposed EVP scheme also aims to minimize the impact of EVP over normal traffic at both stages (i.e., path selection phase and preemption phase). A major advantage of the proposed method is that once the optimal path is selected, the emergency information can be disseminated to other vehicles using vehicle-to-vehicle and vehicle-to-infrastructure communication in the EV path to clear the entire route or the approaching lane. The strategy was tested using a microscopic simulation environment for a real traffic network. The findings indicated a major reduction in the travel time of the EV while minimizing the impact of preemption on the normal traffic. The proposed strategy and evaluation procedure can be helpful for corresponding agencies and practitioners to assess the impact of implementing preemption on existing or proposed arterials. - 2019, The Author(s).Open access funding provided by the Qatar National Library.Scopu
Serial production line performance under random variation:Dealing with the ‘Law of Variability’
Many Queueing Theory and Production Management studies have investigated specific effects of variability on the performance of serial lines since variability has a significant impact on performance. To date, there has been no single summary source of the most relevant research results concerned with variability, particularly as they relate to the need to better understand the ‘Law of Variability’. This paper fills this gap and provides readers the foundational knowledge needed to develop intuition and insights on the complexities of stochastic simple serial lines, and serves as a guide to better understand and manage the effects of variability and design factors related to improving serial production line performance, i.e. throughput, inter-departure time and flow time, under random variation
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